duct should have D 1-0265-1-0267 and from 87 to 98% of it should distil within
1-1-5° ; it should contain only traces of moisture and impurities,
2. Aniline Oils
With aniline oils, besides the above determinations, the proportions of
the various bases present, namely, aniline and o-and p-toluidines are deter-
mined. The estimation may be made by Reinhardt's method,1 which is
based on the fact that, with a mixture of potassium bromide and bromate,
aniline in acid solution is transformed into tribromoaniline, whereas o- and
p-toluidines give dibromo-compounds, and that by oxalic acid in acid
solution, p-toluidine and aniline are precipitated whilst o-toluidine remains
in solution. The procedure is as follows :
(a) DETERMINATION OF THE ANILINE AND OF THE TWO TOLUIDINES TO-
GETHER. The brominating mixture is prepared from 490 grams of bromine,
336 of caustic potash and I litre of water ; the liquid is boiled gently for
2-3 hours and diluted to 9 litres (it should be free from hypobromite).2
To 1-5-2 grams of pure aniline are added 100 c.c. of hydrobromic acid of
D = 1-45-1-48 (or the corresponding quantities of KBr and HC1), the
liquid being diluted with a litre of water and the above brominating solu-
tion added from a burette until a drop of the liquid colours a starch-iodide
paper blue. Division of the amount of aniline taken by the number of c.c.
of the brominating solution required gives the quantity of aniline (t) corre-
sponding with each c.c. of the brominating solution.3 From I- to 2 grams
of the aniline oil are then titrated in the same way, the content in aniline
(x} being calculated from the formulae :
% = 2-3777 v t —1-3777 <*,
so that the percentage (p) of aniline will be
where a = quantity of substance taken.
x = aniline content in a.
v = c.c. of brominating solution used in test.
t = titre in aniline of the brominating solution.
The percentage of the two toluidines together in the oil will be
100 — p.
(b) DETERMINATION OF P-TOLUIDINE WHEN MIXED WITH EITHER ANILINE
OR O-TOLUIDINE OR WITH BOTH BASES. loo grams of the oil are dissolved
in 106 grams of 31% hydrochloric acid (D 1-163) and the liquid poured into
a boiling 10% solution of pure oxalic acid ; 4 the liquid should remain
1 Chem. Zeit, 1893, P- 4*3-
2 An approximately N/y-solution of recrystallised potassium bromate may also be
3 This titre remains moderately constant.
* The quantity of oxalic acid should be greater than that necessary to precipitate
all the p-toluidine present, which may be established by a preliminary experiment.
For oils poor in aniline, about 10 grams of oxalic acid more than is necessary should be
used, and for those richer about 20 grams more. In general, 50 grams of oxalic acid
in 500 c.c. of water may be used for 100 grams of oil.e determined by the method